Shelf



FIG. 1 is a front elevational view of a shelf showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a side view, taken from the left side of FIG. 1, the right side view being a mirror image thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a shelf, as shown and described. 